Compensation Programs (Schedule Of Performance-Based Stock Awards) (Detail) (USD $)	3 Months Ended						12 Months Ended	3 Months Ended							12 Months Ended		3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 2008 [Member]	Mar. 31, 2013 2009 [Member]	Mar. 31, 2013 2010 [Member]	Mar. 31, 2013 2011 [Member]	Mar. 31, 2013 2012 [Member]	Dec. 31, 2012 Performance-Based Stock Awards [Member]	Mar. 31, 2013 Performance-Based Stock Awards [Member] 2008 [Member]		Mar. 31, 2013 Performance-Based Stock Awards [Member] 2009 [Member]		Mar. 31, 2013 Performance-Based Stock Awards [Member] 2010 [Member]	Mar. 31, 2013 Performance-Based Stock Awards [Member] 2011 [Member]	Mar. 31, 2013 Performance-Based Stock Awards [Member] 2012 [Member]	Dec. 31, 2012 Two Thousand and Eight Grants [Member] Performance-Based Stock Awards [Member]	Dec. 31, 2011 Two Thousand and Eight Grants [Member] Performance-Based Stock Awards [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2013 [Member] Performance-Based Stock Awards [Member] 2008 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2013 [Member] Performance-Based Stock Awards [Member] 2009 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2013 [Member] Performance-Based Stock Awards [Member] 2010 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2013 [Member] Performance-Based Stock Awards [Member] 2011 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2013 [Member] Performance-Based Stock Awards [Member] 2012 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2014 [Member] Performance-Based Stock Awards [Member] 2008 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2014 [Member] Performance-Based Stock Awards [Member] 2009 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2014 [Member] Performance-Based Stock Awards [Member] 2010 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2014 [Member] Performance-Based Stock Awards [Member] 2011 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2014 [Member] Performance-Based Stock Awards [Member] 2012 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2015 [Member] Performance-Based Stock Awards [Member] 2008 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2015 [Member] Performance-Based Stock Awards [Member] 2009 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2015 [Member] Performance-Based Stock Awards [Member] 2010 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2015 [Member] Performance-Based Stock Awards [Member] 2011 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2015 [Member] Performance-Based Stock Awards [Member] 2012 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2016 [Member] Performance-Based Stock Awards [Member] 2008 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2016 [Member] Performance-Based Stock Awards [Member] 2009 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2016 [Member] Performance-Based Stock Awards [Member] 2010 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2016 [Member] Performance-Based Stock Awards [Member] 2011 [Member]	Mar. 31, 2013 Remaining Shares With Initial Measurement Periods 2016 [Member] Performance-Based Stock Awards [Member] 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Year of Grant								2008		2009		2010	2011	2012
Grant Date Fair Value Per Share		$ 12.87	$ 11.39	$ 11.64	$ 13.23	$ 13.59		$ 10.18		$ 14.33		$ 12.44	$ 12.72	$ 11.67
Total Original Grants	654,000	225,000	225,000	60,000	72,000	72,000		140,658	[1]	110,917	[2]	128,766	132,490	145,399
Expiration date of grant								Dec. 31, 2015		Dec. 31, 2016		Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2019
Remaining Shares Vesting in Period																		52,915	61,508
Performance-based awards vested, shares							53,431								135,194	135,194								61,499	61,499					63,718	69,853					69,849
Percentage of performance based awards granted, actual							50.00%

[1] The performance criteria for the three-year measurement periods ending December 31, 2012 and 2011 were met resulting in the vesting of 135,194 shares associated with this grant.

[2] (b) The performance criteria for the first three-year measurement period ending December 31, 2012 was met resulting in the vesting of 53,431 shares associated with the first 50% of this grant.